Field
This invention is directed to a biological process for use in removing metallic components from ores by biological techniques. The invention is more particularly directed to the extraction of gallium or germanium from gallium or germanium containing ores.
State of the Art
In the United States, gallium is generally produced as a byproduct of the Bayer process for producing alumina from bauxite and from zinc processing residues. Recently the Apex St. George, Utah mine began operation which recovers gallium and germanium as main products.
The Apex mine holds an ore body which requires a unique recovery process. This ore body is an admixture of waste, dolomite and silica. Valuable elements are found in the jarosite (KFe.sub.3 (SO.sub.4).sub.2 (OH).sub.6), geothite (Fe.sub.2 O.sub.3 *xH.sub.2 O) and quartz (SiO.sub.2) making traditional separation of the mineral from the waste rock very difficult.
The gallium and germanium host materials are
believed to be geothite, limonite (2Fe.sub.2 O.sub.3 *H.sub.2), hematite (Fe.sub.2 O.sub.3), jarosite, azurite (Cu.sub.3 (CO.sub.3).sub.2 (OH).sub.2), malachite (Cu.sub.2 CO.sub.3 (OH).sub.2), conichalcite (CaCu(AsO.sub.4)(OH)) and minor amounts of other metal carbonates, oxides, sulfates, and arsenates. As used herein, "host materials" refer to those ores or similar compounds which have gallium or germanium imbedded therein. Most of the copper-rich ore was removed during previous mining operations and the iron-rich minerals that contain most of the germanium and gallium were rejected as waste. The gallium is generally concentrated in the jarosite.
The Apex mine uses a hydrometallurgical extraction process to recover the metals from the minerals. A "trade-off" exists between necessary leach extraction, the feasibility of separations, corrosiveness to the equipment, and cost.
The process involves leaching with one or more purification steps, and a winning or recovery step. The leaching vessels are arranged in a countercurrent manner to give both good extraction and maximum utilization of reagents. A 40% sulfur dioxide solution at 85% reacts with iron oxide as shown in the following equation: EQU 2FiOOH+SO.sub.2 +2H.sup.+ .dbd.2Fe.sup.30 + +SO.sub.4 +2H.sub.2 O (1)
A solution of gallium, copper, zinc, arsenic in small quantities and large amounts of iron and magnesium results. Copper is removed before the target elements become accessible.
The solution containing the gallium, zinc, arsenic, iron and magnesium is subjected to solvent extraction. The gallium and zinc are transferred by an organophosphorus-kerosene solvent to a fresh sulfuric acid solution. EQU Ga.sup.30.sub.3 +3HX.sub.org .dbd.GaX.sub.3org +3H.sup.+ (2)
Gallium is precipitated by partial neutralization with ammonia after which the precipitate is redissolved and purified. EQU GaCl.sub.3 +3NH.sub.3 +3H.sub.2 O.dbd.Ga(OH).sub.3 +3NH.sub.4 Cl (3)
Gallium metal is then produced in small electrowinning cells.
Calcium fluoride with hydrogen sulfide precipitates germanium. This produces hydrogen fluoride which removes the germanium from the silicates in which it is found.
Bacteria (i.e. Thiobacillus ferrooxidans and Ferrobacillus ferrooxidans) have also been used to extract gallium compounds from gallium containing ore.
As reported in Lundgren et al., "Ore Leaching by Bacteria," Ann Rev. Microbial, 34: 63-83 (1980), Thiobacillus ferrooxidans has been used to oxidize gallium sulfide (Ga.sub.2 S.sub.3) to gallium sulfate (Ga.sub.2 (SO.sub.4).sub.3). Torma in "Oxidation of gallium sulfides by Thiobacillus ferrooxidans", Can J. Microbial, 24: 888-891 (1978), disclosed a method for biomining/bioleaching/ biostabilization by bacterium involving inoculating a quantity of gallium-bearing chalcopyrite concentrate and 70 ml iron-free nutrient medium with prepared T. ferrooxidans. The system is aerated with carbon dioxide (CO.sub.2)-containing air. Distilled water is added to compensate for evaporation, and the pH is maintained at 1.8. The temperature of the reaction is typically 35.degree. C.
The Bacterial Leaching of Metals From Ores, written by G. I. Karaivko, et al. (1977), discloses the use of T. ferrooxidans in leaching non-ferrous metals and sulfides. This article notes that T. ferrooxidans may be used to leach rare metals such as gallium from the crystal structure of many sulfides and non-ferrous metals. The authors suggest a methodology for leaching non-ferrous metals in vats using T. ferrooxidans. The method emphasizes the need for proper aeration, optimal mesh size of ore, pH at about 2.8, and a suggested reaction temperature of approximately room temperature (26.degree. C.).
These and other writings indicate an established study of bioleaching of iron- and sulfur-containing ores, but investigation has been done almost exclusively through the use of Thiobacillus species, particularly T. ferrooxidans.
For example, bioleaching of copper from chalcopyrite containing ore is described in U.S. Pat. No. 4,571,387 to Bruynsteyn, et al. the contents of which are hereby incorporated by this reference. This patent discloses a process for leaching particular metals from ores using sulfide oxidizing bacteria.
"Studies on the Chemoautotrophic Iron Bacterium Ferrobacillus ferrooxidans" by Silverman, et al. (1959) discusses a method for culturing chemoautotrophic bacterium such as Gallionella, T. ferrooxidans, and F. ferrooxidans.
"Microorganisms in Reclamation of Metals" by Hutchins, et al. (40 Ann. Rev. Microbiol. 1986, pp. 311-36), describes various methods of leaching metals from ores using acidophilic iron-oxidizing bacteria. Hutchins further discusses the characteristics of many bacterial forms capable of effectuating bioleaching. Reference is made to bioleaching of Ga.sub.2 S.sub.3 by T. ferrooxidans.
"Biological Leaching: A New Method For Metal Recovery" (B.C. Research; Vancouver, B.C.) provides a general discussion of bioleaching of sulfides in industrial and commercial applications.
"Ore Leaching By Bacteria" by Lundgren, et al. (34 Ann. Rev. Microbiol. 1980, pp. 263-83) details the chemical mechanisms of bioleaching metals from insoluble minerals.
"Bacterial Leaching" by C. Brierley (CRC Critical Reviews in Microbiology, Nov. 1978) discusses industrial applications of bioleaching, with particular emphasis on uranium and copper recovery. Details are provided regarding bacterial efficacy parameters.
"Continuous Bacterial Coal Desulfurization Employing Thiobacillus ferrooxidans" by Myerson, et al. (26 Biotech. and Bioeng. 1984, pp92-99) discusses the increase in bioleaching activity with increase in surface substrate availability.
"Microbiological Mining" by C. L. Brierly (1982) discusses the role played by T. ferrooxidans in leaching copper from low-grade ore on an industrial scale.
"Wastewater Engineering: Treatment, Disposal, Reuse" (McGraw-Hill; 2d Ed, pp. 494-497) discloses
"Biologically Mediated Inconsistencies in Aeration Equipment Performance" by Albertson, et al. (47 Jr. W.P.C.F. No. 5, May 1975, pp. 976-988) provides an evaluation of aeration devices used in biological systems.
The Dorrco Technical Manual, Sec. 32, describes the operation of an agitator--slurry mixer.
"The Bacterial Leaching of Metals from Ores" by Karaivko, et al. (Technicopy Limited, 1977) provides a treatise on bioleaching methodologies, and makes reference to the aqueous migration of gallium in relation to pH values in bioleaching processes.
The use of T. ferrooxidans and F. ferrooxidans has not proven economically useful in extracting gallium and germanium from the ores contained at mines such as the Apex. These bacteria are insufficient to extract the metals at effective (e.g. 95% recovery) levels.